A ternary encapsulation additive for papermaking fillers, its preparation method and application

Abstract

This invention relates to the field of papermaking technology, specifically to a ternary encapsulation agent for papermaking fillers, its preparation method, and its application. The ternary encapsulation agent comprises a first encapsulating agent, a second encapsulating agent, and a third encapsulating agent. The first encapsulating agent is a non-copolymeric cationic polymer with repeating high-cationic and high-amine-group concentration segments. The second encapsulating agent is hyperbranched cationic polyethyleneimine, and the third encapsulating agent is a cationic modified natural polymer compound. In this ternary encapsulation agent, the first encapsulating agent, upon contact with charged calcium carbonate fillers, causes them to aggregate relatively tightly, exhibiting strong shear resistance, which is beneficial for calcium carbonate retention and increases paper ash content. The second encapsulating agent further increases the filler particle size while improving the bonding force with fibers, thus increasing paper strength. The third encapsulating agent improves the bonding force between fibers, further enhancing paper strength.

Description

Technical Field

[0001] This invention relates to the field of papermaking technology, specifically to a ternary encapsulation agent for papermaking fillers, its preparation method, and its application. Background Technology

[0002] Paper is primarily composed of fibers, but for cultural paper, printing paper, decorative base paper, white cardboard, and cigarette paper, fibers alone are insufficient to meet the intended use of the paper; fillers must be added to the pulp. The main functions of adding fillers are: 1. To improve the whiteness, opacity, smoothness, and printability of the paper; 2. To reduce paper deformation, i.e., to improve paper flatness; 3. To reduce the use of fiber raw materials to some extent, thereby lowering production costs.

[0003] The main types of fillers used in papermaking in my country include calcium carbonate, talc, kaolin, titanium dioxide, and iron oxide. Calcium carbonate, especially heavy calcium carbonate (GCC), is the most widely used paper filler due to its readily available and inexpensive raw materials. However, adding too much mineral filler can lead to decreased paper strength and problems such as dusting and linting during printing. Furthermore, mineral fillers have low adhesion, and increasing their amount results in low filler retention, increased filler content in white water, and difficulties in water treatment. Therefore, improving the retention rate of mineral fillers in cellulose fibers, reducing papermaking costs, maintaining or even improving paper strength, and solving problems such as dusting and linting during printing have been persistent challenges for paper manufacturers.

[0004] Numerous reports, both domestically and internationally, have addressed improving filler retention rates. These methods primarily utilize high-molecular-weight polymers such as cationic polyacrylamide, amphoteric polyacrylamide, anionic polyacrylamide, and cationic starch as the main components, combined with auxiliary agents like silica sol, chitosan, and nanocellulose in binary or ternary retention systems to enhance filler retention. For instance, Chinese invention patent CN116905278A employs a ternary retention aid consisting of a first cationic polyacrylamide, a second cationic polyacrylamide, and anionic silica, which can improve the flocculation degree of fibers and fillers, thereby increasing filler retention and reducing white water ash content. Another Chinese invention patent CN119777199A uses cationic modified nanofibers, a cationic buffer solution, and amphoteric high-molecular-weight polyacrylamide to prepare a composite cationic sustained-release solution. This composite cationic sustained-release solution is first reacted with a calcium carbonate suspension and then added to paper fibers to improve calcium carbonate retention. Chinese invention patent CN108138448A uses cationic starch and flocculant to treat filler to form filler flocs, which are then combined with cellulose fibers to form paper pads. This method produces filler flocs with large particle size, improved shear stability, and increased paper strength of the paper pads.

[0005] However, the filler synergists mentioned above are mainly cationic polyacrylamide, which is copolymerized with unsaturated cationic monomers such as acrylamide and allyltrimethylammonium chloride, diallyldimethylammonium chloride, and dimethylaminoethyl methacrylate hydrochloride. The cations are uniformly distributed within the polymer chain segments, resulting in a relatively low density. This leads to insufficient particle size encapsulation for fillers such as calcium carbonate, especially when using light calcium carbonate (PCC) alone or in a mixture of GCC / PCC with a high PCC ratio. The resulting calcium carbonate encapsulated particle size is insufficient, leading to low retention rates. Furthermore, the filler encapsulated by this homopolymeric cationic polyacrylamide is relatively loose and not dense enough, exhibiting poor shear resistance. During the papermaking process of modern high-speed paper machines, the particle size decreases significantly after passing through the high shear of equipment such as pulp pumps and pressure screens, affecting filler retention. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a ternary encapsulation agent for papermaking fillers with good encapsulation effect and strong shear resistance, as well as its preparation method and application.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a ternary encapsulation agent for papermaking fillers, comprising a first encapsulation agent, a second encapsulation agent and a third encapsulation agent, wherein the first encapsulation agent is a non-copolymeric cationic polymer with repeating high cationic concentration segments and high amine concentration segments, the second encapsulation agent is hyperbranched cationic polyethyleneimine, and the third encapsulation agent is a cationic modified natural polymer compound.

[0008] Another technical solution adopted in this invention is: the preparation method of the above-mentioned ternary encapsulation agent for papermaking fillers includes the following steps: preparing a first encapsulating agent, a second encapsulating agent and a third encapsulating agent, and storing the first encapsulating agent, the second encapsulating agent and the third encapsulating agent respectively to obtain the ternary encapsulation agent for papermaking fillers.

[0009] Another technical solution adopted by the present invention is as follows: the application of the above-mentioned ternary coating agent for papermaking fillers in papermaking includes the following steps: adding the first coating agent and the second coating agent to the calcium carbonate solution in sequence to obtain coated calcium carbonate; adding the coated calcium carbonate to the fiber; and finally adding the third coating agent to the mixture of coated calcium carbonate and fiber.

[0010] The beneficial effects of this invention are as follows: The ternary encapsulation agent for papermaking fillers of this invention includes a first encapsulating agent, a second encapsulating agent, and a third encapsulating agent. The first encapsulating agent is a non-copolymeric cationic polymer with repeating high-cationic concentration segments and high-amine concentration segments. After contacting charged calcium carbonate fillers, it causes them to be densely enriched together, exhibiting strong shear resistance, which is beneficial for the retention of calcium carbonate and improves the ash content of the paper. The second encapsulating agent is hyperbranched cationic polyethyleneimine, which can further increase the particle size of the filler while improving the bonding force with fibers and increasing paper strength. The third encapsulating agent is a cationic modified natural polymer compound, which can improve the bonding force between fibers and further improve paper strength. Detailed Implementation

[0011] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments.

[0012] A ternary encapsulation additive for papermaking fillers includes a first encapsulating agent, a second encapsulating agent, and a third encapsulating agent. The first encapsulating agent is a non-copolymeric cationic polymer with repeating high cationic concentration segments and high amine concentration segments. The second encapsulating agent is hyperbranched cationic polyethyleneimine. The third encapsulating agent is a cationic modified natural polymer compound.

[0013] As described above, the beneficial effects of this invention are as follows: The ternary encapsulation agent for papermaking fillers of this invention comprises a non-copolymeric cationic polymer with repeating high cationic concentration segments and high amino concentration segments, hyperbranched cationic polyethyleneimine, and cationic modified natural polymer compounds. The non-copolymeric cationic polymer with repeating high cationic concentration segments and high amino concentration segments has a high local cationic concentration, which, upon contact with negatively charged calcium carbonate filler, causes it to aggregate relatively tightly, resulting in strong shear resistance. After passing through high-shear equipment such as pulp pumps and pressure screens, the particle size does not decrease significantly, which is beneficial for calcium carbonate retention and improves paper ash content. The hyperbranched cationic polyethyleneimine has a large three-dimensional network structure, which can further increase the particle size of calcium carbonate particles flocculated by the first encapsulation agent and firmly bind them in the network, further increasing the shear resistance of the calcium carbonate particles. The polyamine groups and cations of the hyperbranched polymer are excellent cross-linking agents between fibers, which can improve the bonding force with fibers and significantly improve paper strength. The cationic modified natural polymer compounds, when added to cellulose fibers, can improve the bonding force between fibers, further improving paper strength.

[0014] Furthermore, the third encapsulating agent includes at least one of cationic starch, cationic guar gum, and chitosan and its derivatives.

[0015] Furthermore, the degree of substitution of cationic starch is 0.01 to 0.08. Preferably, the degree of substitution of cationic starch is 0.03 to 0.05.

[0016] Furthermore, the molecular weight of cationic guar gum is 100,000 to 1,000,000 Da. Preferably, the molecular weight of cationic guar gum is 400,000 to 600,000 Da.

[0017] Furthermore, the molecular weight of chitosan and its derivatives is 500,000 to 5,000,000 Da. Preferably, the molecular weight of chitosan and its derivatives is 1,000,000 Da to 3,000,000 Da.

[0018] Another technical solution adopted in this invention is: the preparation method of the above-mentioned ternary encapsulation agent for papermaking fillers includes the following steps: preparing a first encapsulating agent, a second encapsulating agent and a third encapsulating agent, and storing the first encapsulating agent, the second encapsulating agent and the third encapsulating agent respectively to obtain the ternary encapsulation agent for papermaking fillers.

[0019] Furthermore, the preparation method of the first encapsulating agent includes the following steps: S1: Initiator and unsaturated gemini cations are added to carry out the reaction; S2: An initiator and an unsaturated polyamine monomer are added to the product of S1 to carry out the reaction; S3: Repeat steps S1 and S2 at least twice to obtain the first encapsulating agent.

[0020] As can be seen from the above description, the first encapsulating agent of the present invention is prepared by segmented dropwise addition of unsaturated gemini cations and unsaturated polyamine monomers, resulting in polymer chains with high cation density segments and high local cation concentrations.

[0021] Furthermore, the mass of the initiator in S1 is 0.01 to 0.5% of the mass of the unsaturated gemini cation, preferably 0.03 to 0.1% of the mass of the unsaturated gemini cation.

[0022] Furthermore, S1 specifically involves: diluting the unsaturated gemini cation and the initiator with deionized water, stirring and heating under N2 protection, and then adding the initiator dropwise to the gemini cation monomer to carry out the reaction.

[0023] Furthermore, the mass of the initiator in S2 is 0.01 to 0.5% of the mass of the unsaturated polyamine monomer, preferably, the mass of the initiator is 0.03 to 0.1% of the mass of the unsaturated polyamine.

[0024] Furthermore, S2 specifically involves diluting the unsaturated polyamine monomer and the initiator with deionized water, then adding them to two constant-pressure dropping funnels. The unsaturated polyamine monomer is added dropwise simultaneously, or the initiator is added dropwise first, and the reaction is carried out under N2 protection with stirring.

[0025] Furthermore, the number of cycles in S3 is 5 to 30 times, preferably 8 to 15 times.

[0026] Furthermore, the molecular structural formula of the unsaturated geminate cation is either structural formula (1) or structural formula (2): Structural formula (1); Structural formula (2).

[0027] Furthermore, the preparation method of the unsaturated gemine cation of structural formula (1) includes the following steps: 1,4-butenediol and 3-chloro-2-hydroxypropyltrimethylammonium chloride are dechlorinated with hydrogen chloride under the catalysis of sodium bicarbonate or sodium hydroxide to obtain the unsaturated gemine cation of structural formula (1), and the chemical equation is as follows, i.e., reaction formula (1): Reaction formula (1).

[0028] Furthermore, the preparation method of the unsaturated gemini cation of structural formula (2) includes the following steps: maleic anhydride and 2,3-epoxypropyltrimethylammonium chloride undergo a ring-opening reaction to obtain the unsaturated gemini cation of structural formula (2), and the chemical equation is as follows, i.e., reaction formula (2): Reaction formula (2).

[0029] Furthermore, the molecular structural formulas of the unsaturated polyamine monomers are structural formula (3) or structural formula (4): Structural formula (3); Structural formula (4).

[0030] As can be seen from the above description, the present invention uses a self-made unsaturated polyamine monomer instead of the commonly used acrylamide. This polymerization reaction is milder and less prone to gelation. Furthermore, the polyamine structure provides more amino imino groups than acrylamide, which can bind more tightly to cellulose fibers through hydrogen bonding, thereby improving paper strength.

[0031] Furthermore, the preparation method of the unsaturated polyamine monomer of structural formula (3) includes the following steps: acryloyl chloride and polyethylene polyamine are reacted with sodium hydroxide to remove hydrogen chloride to obtain the unsaturated polyamine monomer of structural formula (3), and the chemical equation is as follows, i.e., reaction formula (3): Reaction formula (3).

[0032] Furthermore, the preparation method of the unsaturated polyamine monomer of structural formula (4) includes the following steps: allyl glycidyl ether and polyethylene polyamine undergo a ring-opening reaction to obtain the unsaturated polyamine monomer of structural formula (4), and the chemical equation is as follows, i.e., reaction formula (4): Reaction formula (4).

[0033] Furthermore, the polyethylene polyamine is any one of diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.

[0034] Furthermore, the preparation method of the second encapsulating agent includes the following steps: crosslinking branched polyethyleneimine with glycidyl ether, and then adding 2,3-epoxypropyltrimethylammonium chloride to react and obtain the second encapsulating agent.

[0035] Furthermore, the mass ratio of branched polyethyleneimine, glycidyl ether, and 2,3-epoxypropyltrimethylammonium chloride is (80~120):(10~30):(20~50).

[0036] Furthermore, the molecular weight of the branched polyethyleneimine is 600 Da to 10000 Da, preferably 600 Da to 3000 Da.

[0037] Furthermore, the preparation method of the second encapsulating agent includes the following steps: after diluting the branched polyethyleneimine with deionized water, glycidyl ether is slowly added dropwise to the polyethyleneimine aqueous solution, and then 2,3-epoxypropyltrimethylammonium chloride is added to react and obtain the second encapsulating agent.

[0038] Furthermore, the glycidyl ether is a diglycidyl ether and / or a ternary glycidyl ether.

[0039] Furthermore, glycidyl ethers include at least one of diglycidyl ether, ethylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, hexanediol diglycidyl ether, glyceryl triglycidyl ether, and trimethylolpropane triglycidyl ether.

[0040] Furthermore, the preparation method of the third encapsulating agent includes: heating and gelatinizing cationic starch at a certain concentration; diluting cationic guar gum with tap water; and diluting chitosan and its derivatives with tap water. One or two of the above three components are combined to obtain the third encapsulating agent.

[0041] Furthermore, the gelatinization temperature of cationic starch is 85~95℃.

[0042] Another technical solution adopted by the present invention is as follows: the application of the above-mentioned ternary coating agent for papermaking fillers in papermaking includes the following steps: adding the first coating agent and the second coating agent to the calcium carbonate solution in sequence to obtain coated calcium carbonate; adding the coated calcium carbonate to the fiber; and finally adding the third coating agent to the mixture of coated calcium carbonate and fiber.

[0043] Furthermore, the weight ratio of the first encapsulating agent to the second encapsulating agent is 1:2~3.

[0044] Furthermore, the total amount of the first and second encapsulation aids in each ton of calcium carbonate is 1 to 8 kg. Preferably, the total amount of the first and second encapsulation aids in each ton of calcium carbonate is 2 to 5 kg.

[0045] Furthermore, the amount of the third coating agent used per ton of paper is 2-12 kg. Preferably, the amount of the third coating agent used per ton of paper is 4-8 kg.

[0046] As described above, within the recommended range, higher dosages of the first and second coating agents result in higher calcium carbonate retention and greater paper strength. However, exceeding these limits leads to excessively large calcium carbonate particles, reducing paper uniformity and smoothness, thus affecting paper performance and increasing costs. The third coating agent gradually increases paper strength with increasing dosage, but the increase becomes less significant at a certain dosage.

[0047] In the following examples, % refers to mass fraction.

[0048] Embodiment 1 of the present invention is a method for preparing a ternary encapsulation additive for papermaking fillers, comprising the following steps: Step 1: 1. Preparation of the first encapsulating agent: S1: Add 4.4 kg of 1,4-butenediol, 26.86 kg of 3-chloro-2-hydroxypropyltrimethylammonium chloride (70% aqueous solution), and 8.0 kg of 50% sodium hydroxide aqueous solution to the reactor. Heat to 80°C and keep the temperature for 3 hours. Take a sample every half hour to test the pH value. Stop heating when the pH value no longer drops significantly. Turn on the circulating water to cool down to 40°C. Add phosphoric acid and stir to neutralize the pH value to 6.5~7. The unsaturated gemini cationic intermediate A1 (structural formula (1) unsaturated gemini cationic) is obtained.

[0049] S2: 9.05 kg acryloyl chloride, 14.6 kg triethylenetetramine, and 8.0 kg 50 wt% sodium hydroxide aqueous solution were added to the reactor in sequence, stirred and heated to 65°C, and kept at the temperature for 3 hours. The pH value was measured every half hour until the pH value did not decrease significantly. Heating was stopped, and the circulating water was turned on to cool down to 40°C. Phosphoric acid was added and stirred to neutralize the pH value to 6.5~7. 8.5 kg tap water was added and stirred evenly to obtain unsaturated triethylenetetramine intermediate B1 (structural formula (3) unsaturated polyamine monomer).

[0050] S3: Add 4.08 kg of intermediate A1 to the reactor, start stirring and heating, and turn on N2 deoxygenation protection. When the temperature reaches 60℃, add 0.25 kg of 1% ammonium persulfate aqueous solution dropwise, controlling the dropping rate to complete in about 30 minutes, and maintain the temperature for 1 hour. Then add 3.16 kg of intermediate B1 and 0.3 kg of 1% ammonium persulfate aqueous solution dropwise to the reactor, controlling the dropping rate to complete in about 40 minutes, and maintain the temperature for another 1 hour. Then add 4.08 kg of intermediate A1 and 0.25 kg of 1% ammonium persulfate aqueous solution dropwise to the reactor, controlling the dropping rate to complete in about 40 minutes, and maintain the temperature for 1 hour. Then add 3.16 kg of intermediate B1 and 0.3 kg of 1% ammonium persulfate aqueous solution dropwise to the reactor. A 1% ammonium persulfate aqueous solution was added dropwise to the reactor, and the dropping rate was controlled to be completed in about 40 minutes. The reaction was then kept at the temperature for 1 hour. This process of adding dropwise in segments was repeated 8 times. After that, the temperature was kept at the temperature for 3 hours, then cooled to 40°C, the N2 was turned off, and the mixture was filtered to obtain the first encapsulating agent C1.

[0051] 2. Preparation of the second encapsulating agent: 3 kg of branched polyethyleneimine (molecular weight 600 Da) and 4.9 kg of tap water were added to the reactor for dilution. The circulating chilled water was turned on to lower the temperature of the reaction solution to 20°C. 1.6 kg of diglycidyl ether was slowly added dropwise, with the dropping rate controlled according to the temperature inside the reactor, and the temperature was kept below 40°C. After the addition was completed, the temperature was maintained at 40°C for 2 hours. Then, 2.3 kg of 2,3-epoxypropyltrimethylammonium chloride was dissolved in 2 kg of tap water and slowly added dropwise to the reactor over a period of about 1.5 hours. After the addition was completed, the reaction was maintained at 40°C for 2 hours to obtain the second encapsulating agent D1.

[0052] 2. Preparation of the third encapsulating agent: The third coating agent is cationic starch. 48 kg of tap water was added to the reactor, along with 2 kg of cationic starch with a degree of substitution of 0.03. Stirring and heating were started, and the temperature was raised to 95°C. The mixture was kept at this temperature for 1 hour to gelatinize. The temperature was then lowered to 75°C and kept at this temperature for later use, thus obtaining the third coating agent E1.

[0053] Embodiment 2 of the present invention is a method for preparing a ternary encapsulation additive for papermaking fillers, comprising the following steps: 1. Preparation of the first encapsulating agent: S1: Add 5kg of tap water and 15.2kg of 2,3-epoxypropyltrimethylammonium chloride to the reactor. Turn on the refrigeration machine to lower the temperature of the reactor to 15°C. Add 4.3kg of 1,4-butene diamine in batches and slowly drop it. Control the dropping speed and keep the reaction temperature below 30°C. After the dropping is completed, keep the reaction at 30°C for 3 hours. Then add 14.5kg of tap water and stir to dilute it to obtain unsaturated gemini cationic intermediate A2 (structural formula (2) unsaturated gemini cationic).

[0054] S2: Add 5.7 kg of allyl alcohol glycidyl ether and 5.0 kg of tap water to the reactor, turn on the circulating chilled water, and lower the temperature of the reactor to 20°C. While stirring, slowly add 9.5 kg of tetraethylenepentamine liquid, and control the reaction temperature to not exceed 40°C. After the addition is complete, keep the reaction at 40°C for 3 hours, then add 10.2 kg of tap water to dilute and stir evenly to obtain unsaturated triethylenetetramine intermediate B2 (structural formula (4) unsaturated polyamine monomer).

[0055] S3: Add 3.45 kg of intermediate A2 to the reactor, start stirring and heating, and turn on N2 deoxygenation protection. When the temperature reaches 60℃, add 0.3 kg of 1% potassium persulfate aqueous solution dropwise, controlling the dropping rate to complete in about 30 minutes, and maintain the temperature for 1 hour. Then add 4.06 kg of diluted intermediate B2 and 0.2 kg of 1% potassium persulfate aqueous solution dropwise to the reactor, controlling the dropping rate to complete in about 40 minutes, and maintain the temperature for 1 hour again. Then add 3.45 kg of intermediate A2 and 0.3 kg of 1% potassium persulfate aqueous solution dropwise to the reactor, controlling the dropping rate to complete in about 40 minutes, and maintain the temperature for 1 hour. Finally, add 4.06 kg of diluted intermediate B2 and 0.2 kg of 1% potassium persulfate aqueous solution dropwise to the reactor. A 1% potassium persulfate aqueous solution was added dropwise to the reactor, and the dropping rate was controlled to be completed in about 40 minutes. The reaction was then kept at the temperature for 1 hour. This process of adding dropwise in segments was repeated 8 times. After that, the temperature was kept at the temperature for 3 hours, then cooled to 40°C, the N2 was turned off, and the mixture was filtered to obtain the first encapsulating agent C2.

[0056] 2. Preparation of the second encapsulating agent: 4.0 kg of tap water and 2.7 kg of branched polyethyleneimine (molecular weight 1200 Da) were added to a reactor and stirred to dissolve. The circulating chilled water was turned on to lower the temperature of the reaction solution to 20°C. 1.35 kg of diglycidyl ether was slowly added dropwise, with the dropping rate controlled according to the temperature inside the reactor, and the temperature was kept below 40°C. After the addition was completed, the temperature was maintained at 40°C for 2 hours. Then, 2.1 kg of 2,3-epoxypropyltrimethylammonium chloride was dissolved in 2.15 kg of tap water and slowly added dropwise to the reactor over a period of about 1.5 hours. After the addition was completed, the reaction was maintained at 40°C for 2 hours to obtain the second encapsulating agent D2.

[0057] 3. Preparation of the third encapsulating agent Add 48 kg of tap water to the reactor, and while stirring, add 2 kg of cationic guar gum (molecular weight 500,000 Da). Turn on the heater to raise the temperature to 50°C, and stir until the guar gum is completely dissolved. Keep it warm for later use to obtain the third encapsulating agent E2.

[0058] Embodiment 3 of the present invention is a method for preparing a ternary encapsulation additive for papermaking fillers, comprising the following steps: 1. Preparation of the first encapsulating agent: The preparation method of the first encapsulation agent in this embodiment 3 differs from that of C1 in embodiment 1 only in that the number of repetitions of step S3 in embodiment 1 is increased to 12 times, resulting in a non-copolymeric cationic polymer C3 with a higher molecular weight.

[0059] 2. Preparation of the second encapsulating agent: 4.86 kg of tap water and 2.7 kg of branched polyethyleneimine (molecular weight 1800 Da) were added to a reactor and stirred until completely dissolved. The circulating chilled water was turned on to lower the temperature of the reaction solution to 20°C. 1.56 kg of glycerol triglycidyl ether was slowly added dropwise, with the dropping rate controlled according to the temperature inside the reactor, and the temperature was kept below 40°C. After the addition was completed, the reaction was maintained at 40°C for 2 hours. Then, 1.8 kg of 3-epoxypropyltrimethylammonium chloride was diluted with 1.2 kg of tap water and added dropwise to the reactor over a period of about 1.5 hours. After the addition was completed, the reaction was maintained at 40°C for 2 hours to obtain the second encapsulating agent D3.

[0060] 3. Preparation of the third encapsulating agent Add 48 kg of tap water to the reactor, and while stirring, add 2 kg of chitosan solid (molecular weight 1,000,000 Da). Add dilute hydrochloric acid dropwise to adjust the pH value to 5.0, add 100 ppm of chitosanase, turn on the heater to raise the temperature of the reactor to 50°C, keep it at that temperature for 3 hours, and add 10% sodium hydroxide aqueous solution dropwise until the pH reaches 7.0 to terminate the reaction, thus obtaining the third encapsulating agent E3.

[0061] Embodiment four of the present invention is a method for preparing a ternary encapsulation additive for papermaking fillers, comprising the following steps: 1. Preparation of the first encapsulating agent: The preparation method of the first encapsulation agent in Example 4 differs from that of C2 in Example 2 only in that the number of repetitions of step S3 in Example 2 is increased to 15 times, resulting in a non-copolymeric cationic polymer C4 with a higher molecular weight.

[0062] 2. Preparation of the second encapsulating agent: The second encapsulation agent in Example 4 is prepared differently from D3 in Example 3, except that the mass of 3-epoxypropyltrimethylammonium chloride is increased to 2.2 kg, resulting in hyperbranched cationic polyethyleneimine D4 with higher cationicity.

[0063] 3. Preparation of the third encapsulating agent The third encapsulating agent in this fourth example differs from E3 in the preparation method only in that the molecular weight of chitosan is changed to 3,000,000 Da, resulting in a chitosan solution E4 with a higher molecular weight.

[0064] Comparative Example 1 of the present invention is: The only difference between Comparative Example 1 and Example 1 is that the first encapsulating agent step S3 was not added in stages. Instead, A1 and A2 were added to the reactor simultaneously in proportion, and the initiator was added dropwise to carry out the polymerization reaction to obtain C5.

[0065] C5, D1, and E1 together form a ternary encapsulation additive for papermaking fillers.

[0066] Comparative Example 2 of the present invention is as follows: The difference between Comparative Example 2 and Example 2 is as follows: In the preparation of the second encapsulating agent, 4.0 kg of tap water and 2.7 kg of branched polyethyleneimine (molecular weight 1200) were added to the reaction vessel and stirred until completely dissolved. The circulating chilled water was turned on to lower the temperature of the reaction solution to 20°C. No cross-linking reaction was carried out. 2.1 kg of 3-epoxypropyltrimethylammonium chloride aqueous solution diluted with 2.15 kg of tap water was added dropwise. The addition was completed in about 1.5 hours. After the addition was completed, the reaction was kept at the temperature for 2 hours to obtain the second encapsulating agent D5.

[0067] D5, along with C2 and E2, forms a ternary encapsulation additive for papermaking fillers.

[0068] Comparative Example 3 of the present invention is as follows: A binary encapsulation agent was obtained by replacing the first and second encapsulation agents of the present invention with commercially available cationic polyacrylamide (Henan Liansheng Environmental Protection Technology Co., Ltd., molecular weight 800W) and combining it with the third encapsulation agent E1 of Example 1 of the present invention.

[0069] Example 5 of the present invention is: a ternary encapsulation agent for papermaking fillers prepared by the preparation method of Example 1.

[0070] Embodiment six of the present invention is: a method for applying a ternary encapsulation agent for papermaking fillers to improve the calcium carbonate retention rate of paper, the specific implementation method of which is as follows: S1; Preparation of calcium carbonate encapsulating agent: Dilute the first encapsulating agent C1~C5 and the second encapsulating agent D1~D5 in Examples 1~4, Comparative Example 1 and Comparative Example 2 with tap water by 100 times respectively, and stir well for later use.

[0071] S2: Fiber preparation: Place 3 kg of 1% fiber into a fiber dissociator and dissociate it at a speed of 3000 r / min for 20 min, then set aside.

[0072] S3: Mixing calcium carbonate and encapsulating agent: Prepare a 1% calcium carbonate dilution (GCC and PCC mass ratio 1:1) for later use. Accurately weigh 100g of 1% calcium carbonate liquid, and use a micropipette to measure 100μl of the C1 dilution prepared in step S1. Place it in a disperser and stir at 1500r / min for 1min. Then add 200μl of the D1 dilution prepared in step S1, and place it in a disperser and stir again at 1500r / min for 1min to obtain the encapsulated calcium carbonate flocculent solution F1. Following the above steps, prepare calcium carbonate flocculent solutions F2~F6 using C2 and D2, C3 and D3, C4 and D4, C5 and D1, and C2 and D6 respectively.

[0073] S4: Sheet making: Weigh 300ml of the dissociated fiber prepared in step S2 into a 1L beaker, add the coated calcium carbonate flocculant F1 prepared in step S3, wash the calcium carbonate adhering to the bottle wall with water, then pour it into the beaker, add 18ul of the third coating agent E1 with a micropipette, place it in a disperser and stir at 1500r / min for 3min, add water to 1L, stir with a glass rod for about 2min, pour it into a paper forming device to make sheets, repeat the sheet making process 3 times for each sample to obtain three sheets of paper.

[0074] S5: Testing: Place the prepared sheets in an oven at 110±5℃ for 30 minutes (15 minutes for each side). Remove them and place them in a constant temperature and humidity environment (temperature 25±2℃, humidity 50±5%) for 24 hours. Test the basis weight, bursting strength, ring crush, ash content, and other indicators. The average value of the test data for three sheets of paper for each sample is taken. The test results are shown in Table 1. The test data of the paper sheets made using the ternary coating agent of papermaking filler in Examples 1 to 4 are numbered G1 to G4, respectively. The test data of the paper sheets made using the ternary coating agent in Comparative Examples 1 and 2 are numbered G5 to G6, respectively.

[0075] S6: Commonly available cationic polyacrylamide (Henan Liansheng Environmental Protection Technology Co., Ltd., molecular weight 800W) is diluted to a 1% aqueous solution and replaced with the first and second encapsulation aids of the present invention in equal effective amounts. Following steps S1 to S3, calcium carbonate flocculant F7 is prepared and then combined with the third encapsulation aid E1 of Example 1 of the present invention to obtain a binary encapsulation aid. Paper sheet is formed according to step S4, and the test data of the obtained paper sheet is numbered G7.

[0076] Table 1 As can be seen from the test results in Table 1, in the blank stage without additives, the interlayer bonding, tensile strength, flexural endurance, and ash content are all relatively low, and the calcium carbonate particle size D is also low. 50 The particle size is only 1.674. After adding G1 and G2 paper filling agents with ternary coating, the particle size of calcium carbonate is significantly increased after coating, thus significantly improving the ash content and basis weight of the paper. While improving the ash content, the three paper strength indicators, interlayer bonding strength, tack strength, and folding endurance, also show significant improvement. In G3 and G4, the molecular weight of the first coating agent increases with the number of staged drops, and the second coating agent increases the molecular weight of branched polyethyleneimine, further increasing the particle size of calcium carbonate coating. The paper basis weight and ash content are further improved compared to G1 and G2. In particular, in G4, the second coating agent D4 increases the cationicity, and the molecular weight of chitosan in the third coating agent E4 increases to 3,000,000 kDa, resulting in a significant improvement in the ash content and various strength indicators of the paper. In G5, the first coating agent C5 was not added in stages, resulting in calcium carbonate flocculent particle size similar to G1. However, the ash content and basis weight were significantly lower than G1, indicating that the well-flocculated calcium carbonate underwent multiple high-speed dispersions during papermaking, leading to a decrease in particle size and retention rate. The strength index was also slightly lower than G1. In G6, the branched polyethyleneimine in the second coating agent D5 was not cross-linked and had a low molecular weight, resulting in a significant decrease in calcium carbonate particle size, paper ash content, basis weight, and strength. In G7, a binary coating agent composed of commercially available cationic polyacrylamide and cationic starch was used, but the improvement in ash content and strength compared to the control was not significant.

[0077] In summary, the ternary encapsulation additive for papermaking fillers, its preparation method, and its application provided by this invention have the following advantages: ①The first encapsulating agent of this invention adopts a segmented dropwise addition method of geminal cationic and unsaturated polyamine. The resulting polymer chain segments contain high cationic density segments. When they come into contact with charged calcium carbonate filler, they are enriched together relatively tightly, which has strong shear resistance, which is conducive to the retention of calcium carbonate and improves the ash content of paper.

[0078] ②The second encapsulating agent of the present invention, hyperbranched cationic polyethyleneimine, can further increase the particle size of the filler while improving the bonding force with the fiber and increasing the paper strength.

[0079] ③The third coating agent of this invention can improve the bonding force between fibers and further improve the paper strength.

[0080] ④ This invention uses a self-made unsaturated polyamine monomer instead of the commonly used acrylamide. This polymerization reaction is milder and less prone to gelation. Furthermore, the polyamine structure provides more amino and imino groups than acrylamide, which can bind more tightly to cellulose fibers through hydrogen bonding, thereby improving paper strength.

[0081] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made using the present invention specification, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A ternary encapsulation additive for papermaking fillers, characterized in that, It includes a first encapsulating agent, a second encapsulating agent, and a third encapsulating agent. The first encapsulating agent is a copolymer cationic polymer with repeating high cationic concentration segments and high amino concentration segments. The second encapsulating agent is hyperbranched cationic polyethyleneimine. The third encapsulating agent is a cationic modified natural polymer compound. The preparation method of the first encapsulating agent includes the following steps: S1: Initiator and unsaturated gemini cations are added to carry out the reaction; S2: An initiator and an unsaturated polyamine monomer are added to the product of S1 to carry out the reaction; S3: Repeat steps S1 and S2 at least twice to obtain the first encapsulating agent; The molecular structure of the unsaturated geminate cation is either structure (1) or structure (2): Structural formula (1); Structural formula (2); The molecular structural formula of the unsaturated polyamine monomer is structural formula (3) or structural formula (4): Structural formula (3); Structural formula (4); The second encapsulating agent has a hyperbranched cationic polyethyleneimine with a large three-dimensional network structure. The preparation method includes the following steps: crosslinking branched polyethyleneimine with glycidyl ether, and then adding 2,3-epoxypropyltrimethylammonium chloride to react and obtain the second encapsulating agent.

2. The ternary encapsulation additive for papermaking fillers according to claim 1, characterized in that, The third encapsulating agent includes at least one of cationic starch, cationic guar gum, and chitosan and its derivatives.

3. The preparation method of the ternary encapsulation additive for papermaking fillers as described in claim 1 or 2, characterized in that, Includes the following steps: A first encapsulating agent, a second encapsulating agent, and a third encapsulating agent are prepared and stored separately to obtain a ternary encapsulation additive for papermaking fillers.

4. The preparation method of the ternary encapsulation additive for papermaking fillers according to claim 1, characterized in that, The mass ratio of branched polyethyleneimine, glycidyl ether and 2,3-epoxypropyltrimethylammonium chloride is (80~120):(10~30):(20~50).

5. The preparation method of the ternary encapsulation additive for papermaking fillers according to claim 4, characterized in that, The glycidyl ether is a binary glycidyl ether or a ternary glycidyl ether.

6. The application of the ternary encapsulation additive for papermaking fillers as described in claim 1 or 2 in papermaking, characterized in that, Includes the following steps: The first encapsulating agent and the second encapsulating agent were added to the calcium carbonate solution in sequence to obtain encapsulated calcium carbonate; The coated calcium carbonate is added to the fiber; finally, a third coating agent is added to the mixture of coated calcium carbonate and fiber.

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